Apparatus and methods for tensioning cables

ABSTRACT

A hydraulic jack is disclosed for simultaneously tensioning a plurality of reinforcing cables anchored to a structure by means of an anchor plate and anchor wedges seated in corresponding seats in the anchor plate. An aligning template is provided for aligning the cables with a tensioning head assembly in the jack, thereby facilitating placement of the jack on the cables. The tensioning head assembly includes a gripping plate having a bore for each cable with each bore having a wedge-shaped seat to receive gripping jaws biased towards the seat. The assembly further includes an unclamping plate, mounted in one embodiment for movement with the gripping plate, provided for dislodging the gripping jaws from their seats to release the cables after tensioning. The tensioning head assembly is mounted at one end of an hydraulically actuated plunger and is urged away from the structure to seat the gripping jaws about the cables and thereafter tension the cables. An hydraulically actuated striker assembly operates to seat the anchor wedges in the anchor plate after tensioning is completed. In one embodiment, the aligning template is received within the front end of the jack and serves as a striker plate in transmitting the seating force from the striker assembly to the anchor wedges.

Surriloas et a1.

[ APPARATUS AND METHODS FOR TENSlONlNG CABLES [76] Inventors: Jorge Juan Ventura Surribas, Calle San Andres, 240; Juan Coll Morell, Calle Amilcar, 209, both of Barcelona, Spain 22 Filed: Sept. 12, 1972 21 Appl. No.: 288,415

[30] Foreign Application Priority Data Primary Examiner-Al Lawrence Smith Assistant ExaminerRobert C. Watson Attorney, Agent, or FirmBrumbaugh, Graves, Donohue & Raymond [451 Oct. 29, 1974 [5 7 ABSTRACT A hydraulic jack is disclosed for simultaneously tensioning a plurality of reinforcing cables anchored to a structure by means of an anchor plate and anchor wedges seated in corresponding seats in the anchor plate. An aligning template is provided for aligning the cables with a tensioning head assembly in the jack, thereby facilitating placement of the jack on the cables. The tensioning head assembly includes a gripping plate having a bore for each cable with each bore having a wedge-shaped seat to receive gripping jaws biased towards the seat. The assembly further includes an unclamping plate, mounted in one embodiment for movement with the gripping plate, provided for dislodging the gripping jaws from their seats to release the cables after tensioning. The tensioning head assembly is mounted at one end of an hydraulically actuated plunger and is urged away from the structure to seat the gripping jaws about the cables and thereafter tension the cables. An hydraulically actuated striker assembly operates to seat the anchor wedges in the anchor plate after tensioning is completed. In one embodiment, the aligning template is received within the front end of the jack and serves as a striker plate in transmitting the seating force from the' striker assembly to the anchor wedges.

18 Claims, 4 Drawing Figures APPARATUS AND METHODS FOR-TENSIONING CABLES BACKGROUND OF THE INVENTION This invention relates to a hydraulic jack for simultaneously tensioning a plurality of reinforcing rods, cables, wires or the like protruding from an anchor assembly which anchors the cables to a structure.

Hydraulic jacks currently used for this purpose are constituted by hollow cylinders to which is coupled a special device for supplying the traction force and effecting the further operations necessary for this purpose. However these jacks used complicated and expensive mechanisms and are difficult to maintain and repair. Furthermore, all of the preassembled jacks presently available are difficult to use because of the problem of properly threading the jack on the rods. The rods, which may number from fifty to a hundred, are frequently too unwieldly to work with easily. Also, a jack suitable for tensioning this many rods is necessarily quite large and heavy. As a result of all these factors, it is quite difficult to thread the rods extending from the anchoring assembly into the corresponding gripping jaws of the tensioning head assembly.

SUMMARY OF THE INVENTION It is accordingly an object of the invention to provide a hydraulic jack which is of simple and practical design.

It is a further object to provide a hydraulic jack for tensioning reinforcing cables and the like which is extremely light and acceptably economical.

It is a further object of the invention to provide a hydraulic jack having only three fluid working spaces by means of which it is possible to effect all the necessary operations for tensioning the cables or the like, locking or unlocking of the jaws or wedges of the tensioning head assembly and of the anchoring plate.

It is yet a further object of the invention to provide a hydraulic jack having an aligning template which is placed on the cables prior to positioning the jack on the cables for aligning the cables for insertion into the gripping jaws of the tensioning head assembly.

In accordance with the invention, a hydraulic jack for simultaneously tensioning a plurality of cables is provided which includes a jack body enclosing a tensioning head having gripping jaws for tensioning the cables and a striker assembly for driving the anchor wedges into their seats after tensioning. Further, an aligning template is provided which has a plurality of bores arranged in a pattern corresponding to that of the gripping jaws and adapted to be threaded onto the cables independently of the housing and positioned closely adjacent the free ends of the cables to align the cable ends in the pattern of the gripping jaws, whereby upon insertion of the jack body over the cables, the cable ends are held by the plate in proper alignment for receipt by the gripping jaws.

As another feature of the invention, an unclamping plate is provided for unseating the gripping jaws after tensioning is completed. The unclamping plate may or may not be secured to the gripping plate, and is arranged to effect the unseating operation upon return of the tensioning head assembly to the forward cablegripping position.

The jack body has at one end thereof a mouth for bearing against the anchor assembly and has a passage extending longitudinally from the mouth to the other end thereof.

The tensioning head assembly forms the front end of a plunger slidable within the passage and has gripping jaws to receive end portions of the cables. The plunger has a first external step and the passage has a corresponding first internal step facing the first external step. The first external step and the first internal step form the opposite ends of a first fluid-tight expansible pressure chamber between the plunger and the jack body. The plunger further has a second external step and the passage has a second internal step facing the second external step. The second external step and the second internal step form opposite ends of a second fluid-tight expansible pressure chamber between the plunger and the jack body. By introducing hydraulic fluid into the first pressure chamber the plungeris moved away from the mouth and by introducing hydraulic fluid into the second pressure chamber the plunger is moved towards the mouth.

The striker assembly is also mounted for slidable movement in the longitudinal passage and includes a striker piston which has a third external step corresponding to a third internal step of the passage facing said external step. The third external step and the third internal step form the opposite ends of a third fluidtight expansible pressure chamber between the striker piston and the jack body. By introducing hydraulic fluid into the third pressure chamber the striker assembly is moved towards the mouth to drive the anchor wedges into their corresponding seats in the anchor plate.

Further, an unclamping plate slidably attached to the gripping plate on the side thereof facing the mouth for engaging a stop means upon movement of the plunger towards the mouth to release the gripping jaws from the cables.

An aligning template removably received by the jack mouth is provided for aligning the cables for receipt by the tensioning head.

BRIEF DESCRIPTION OF THE DRAWINGS In order that the invention may be clearly understood and readily carried into effect, some preferred embodiments thereof will now be described, by way of example only, with reference to the accompanying drawings, wherein:

FIG. 1 shows a longitudinal view partially in section of a hydraulic jack in accordance with the invention;

FIG. 2 shows the position of the jack and the aligning template prior to insertion of the jack on the rods;

FIG. 3 shows a detailed view in section with parts cut away of a device used for unclamping the gripping jaws; and

FIG. 4 shows a detaled view in section with parts cut away of another device for unclamping the gripping aws.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Referring to the drawings, and to FIG. 1 in particular, the hydraulic jack 20 comprises a jack body formed by annular members 21, 22 and 23. The member 23 dcfines a mouth at the front end of the jack body into which opens a longitudinal passage extending through the jack body. Members 21 and 22 are held together in end-to-end axial alignment by bolts 24 and mouth 23 is similarly attached to member 21 by bolts 25. A tubular plunger 26, which for convenience may have forward and rearward portions 26a and 26b, is disposed within the longitudinal passage formed by annular members 21 and 22 for slidable movement therein.

The member 22 of the jack body is provided at its inner end, i.e., the end attached to annular member 21, with an inwardly directed flange 27 and at its other end with an inwardly directed member 28. An annular pressure chamber 29 is formed by plunger 26, member 22, flange 27 and member 28. The plunger 26 has an annular shoulder 30 extending into the chamber 29 which forms a hydraulic piston for driving the plunger.

Ducts 31 and 32 are provided at the rearward and forward ends, respectively, of the chamber 29. An appropriate hydraulic fluid can be injected (by means not shown) through either the duct 31 or duct 32 to cause displacement of the plunger 26 either forwardly or rearwardly. The chamber 29 is sealed at both ends by O-rings 33 and 34. The O-ring 35 seals the space between member 28 and member 22.

The member 28 also acts as a stop for limiting the rearward movement of plunger 26 and further provides structure for closing the opening at the rearward end of the jack.

The front end of plunger 26 is provided with an internal screw thread 36 with which engages an externally threaded gripping plate 37. Plate 37 is formed with a plurality of longitudinal, generally wedge shaped orifices or bores 38 in which are lodged, during the tensioning of cables 39, a plurality of cable gripping jaws 40 of the conical-wedge type. Each cable passes through a bore 38 and the associated jaws 40. The jaws 40 for each cable 39 are urged towards the seatings formed by the conical bores 38 in the gripping plate 37 in order to grip the cables 39 by means of a pressure mechanism provided at the base of each jaw 40. This pressure mechanism comprises a plurality of spring like conical discs or washers 41 which are disposed on a tubular member 42 fastened to the base of each jaw 40. The free ends of the members 42 slidably extend through bores 43 formed in a pressure plate 44 which acts as a stop element for the discs 41 so that the mechanism affords the necessary pressure on the base of the jaws 40. Lock washers prevent the members 42 from slipping through the orifices 43 when the wedges are in their extreme forward positions. A spacer 45 and bolt 46 (only one of which is shown) are provided for holding the plate 44 a preselected distance rearwardly of the gripping plate 37.

For unclamping the jaws 40 from the cables after completion of the job, an unclamping plate 47 is disposed adjacent the front end of plunger 26. In a preferred embodiment, (See FIG. 3) this unclamping plate 47 is mounted to the gripping plate 37 by means of bolts 48 (only one of which is shown) through counter bores 49 and bores 50 so that plate 47 may freely slide on the bolts 48 relative to the gripping plate 37, but the forward movement of the plate 47 relative to the gripper plate 37 is limited by the heads of bolts 48 abutting the inner surfaces of the counter bores 49.

The unclamping plate 47 is provided with a plurality of bores 47a arranged in a pattern corresponding to that of the gripping jaws 40 and aligned therewith. Within each bore 470 a hollow stub 51 (See FIG. 3) is mounted in a recess 52 and held in place by cover plate 53 attached to plate 47 by screw 54 (See H0. 1). These stubs are located opposite the bores 38 formed in plate 37. A spring 55 which surrounds each stub 51 and sits in a recess 56 in gripping plate 37 provides a biasing force acting to separate the unclamping plate 47 and the gripping plate 37. The hollow stubs 51 are dimensioned so that when the unclamping plate 47 and gripping plate 37 are forced together by means which will be described subsequently, the stubs 51 enter the bores 38 and push the wedges or jaws 40 out of their corresponding seats whereby the cables 39 are released from the jaws 40.

Another mechanism for unclamping the jack from the cables 39 is shown in FIG. 4. The conical discs 41 are disposed on tubular members 42' fastened to the bases of jaws 40. The members 42' extend through the pressure plate 44 and further extend through a pulling plate 57. The members 42 have lips 58 at their rearward ends for engaging the pulling plate 57. Means (schematically shown in FIG. 4 as a hydraulic piston means 59) are provided for selectively moving the pulling plate 57 away from the gripping plate 37 whereupon the tubular members 42 cause the jaws 40 to be extracted from their wedge shaped bores 38 to release the cables 39.

Referring again to FIG. 1, a striker assembly including a striker piston 60 and a striker member 61 is located adjacent the mouth 23 of the jack. The piston 60 is driven forward by hydraulic fluid injected into chamber 62 through conduit 63 located in member 21 of the jack body. The chamber 62 is hydraulically sealed by O-rings 64 and 65.

A removable striker plate 66 received by the mouth 23 has a series of bores 67 arranged in a pattern corresponding to that of the bores 38 in the gripping plate 37. The piston 60, acting through member 61, drives the striker plate 66 forward when hydraulic fluid is injected into chamber 62 to drive the anchor wedges 68 into their corresponding seats 69 in anchor plate 70. The anchor plate and wedges, comprising the anchor assembly, anchor the reinforcing rods or cables 39 in their tensioned state to trumpets 71 embedded in structure 72 which, for example, may be a concrete beam.

An annular ring 73 surrounds the anchor plate and provides an abutting surface for the mouth 23 of the jack during tensioning. The mouth 23 has a lip 23a for limiting the rearward movement of the anchor plate 70 when the tensioning head moves rearwardly to tension the cables.

The member 61 is mounted for limited longitudinal movement by means of bolt 74 positioned in a recess 75. A spring 76 biases the member 61 in a rearward direction so that during tensioning the striker plate 66 may move away from abutment with anchor wedges 68 thus permitting these wedges to be moved out of their corresponding anchor seats by the cables being pulled through them. With this arrangement the cables 39 can slide through the anchor wedges 68 during tensioning.

The striker plate 66 also functions as an aligning template when the jack is to be used. For this purpose, the plate 66 is removed from the jack prior to threading the jack on the cables and is placed on the cables 39 extending from the anchor assembly as shown in FIG. 2. The striker plate or aligning template 66 has a plurality of bores 67 arranged in a pattern corresponding to that of the gripping jaws. By independently threading this plate on the cables and positioning the plate adjacent the free ends of the cables, the cable ends are arranged in a pattern corresponding to that of the tensioning head comprising the gripping plate 37 and wedges 40 together with unclamping plate 47 mounted to the front of the gripping plate. When the jack body is mounted on the cables, the cable ends are held by the plate 66 in proper alignment for receipt by the unclamping plate 47 which by means of hollow stubs 51 guides the cables into the gripping jaws 40.

By placing the plate 66 on the ends of the cables prior to mounting the jack, the cable ends are aligned so that the jack may be easily inserted on the cables. If the plate 66 were threaded on the cables and moved to abut the anchor plate 70 before the jack was mounted on the cables, the operator would have to thread the gripping jaws of the jack itself on the cables which is a very cumbersome process. Having a striker plate which is removable also overcomes the difficulty of having to thread the entire jack on the cables.

Before the jack is mounted on the cables the centering member 73 is positioned around the anchor plate 70 so as to abut the trumpet 71. To prepare the jack for mounting on the cables hydraulic fluid is injected through duct 31 into chamber 29 for driving the plunger 26 towards the mouth. This causes the jaws 60 to be opened by stubs 511 and also positions the tensioning head at the front end of the jack so that when the jack is positioned directly in front of the aligned cables, the alignment plate 66 and the tensioning head are in close spaced relation.

Next the jack 20 is introduced over the aligned free ends of the cables 39. Hydraulic fluid is then introduced through the duct 32 whereupon plunger 26 is moved away from the mouth 23. The jaws 40 are automatically driven into their seatings in the bores 38 by the conical discs 41 to grip the reinforcing cables 39. The unclamping stubs 51 in FIG. 1 are withdrawn automatically from the bores 38 by springs 55. When the desired tension in the cables 39 has been achieved, hydraulic fluid is admitted under pressure through the inlet 63 to cause piston 60 to drive plate 66 towards the anchor plate 70 thereby seating the wedges 68 to lock the cables 39 to the anchoring plate in their tensioned state.

During tensioning the unclamping plate 47 moves with the plunger 26 but the unclamping plate 47 and the gripping plate 37 are separated as shown in FIG. 3.

When the gripping jaws W are to be unclamped to remove the jack from the cables, hydraulic fluid is introduced through duct 31 into chamber 29. The plunger 26 is thereby driven towards the mouth 23 of the jack. As the unclamping plate 47 approaches the forward end of the jack, it strikes the stop member '77 mounted on the mouth 23 and slidably extending through the striker member 61. The gripping plate 37 continues to be driven forward by the hydraulic force until it abuts the unclamping plate 47. As this occurs the stubs 51 enter the bores 38 pushing the jaws 40 out of their seats. This arrangement is depicted in FIG. 1. By keeping the duct 31 coupled to a hydraulic pressure source, the jack may now be removed from the cables.

lf, however, the desired tensioning is not achieved on the first stroke, hydraulic fluid is again injected through duct 32 and the process is started over again. This process may be repeated as many times as necessary.

If the unclamping mechanism as shown in FIG. 4 is used, the jaws 40 can be withdrawn from their wedgeshaped seats 38 by moving the pulling plate 57 away from the gripping plate 37 by means of hydraulic piston 59 thereby drawing the jaws 40 from their bores 38.

Although the plunger 26 has been shown as a hollow body, it would be possible for this to be a solid body having a cavity therein for lodging the free ends of the cables 39, thereby considerably simplifying the machining work required.

While the fundamental novel features of the invention have been shown and described, it will be understood that various substitutions, modifications and variations may be made by those skilled in the art without departing from the spirit and scope of the invention. Accordingly, all such modifications and variations are included within the intended scope of the invention as defined by the following claims.

What is claimed is:

l. A jack for simultaneously tensioning a plurality of cables each projecting through a wedge-shaped bore in an anchor assembly and for anchoring the cables to a structure after tensioning by seating anchor wedges in the corresponding wedge-shaped bores, comprising:

a jack body having a front end for operatively abutting the structure during tensioning, and further having a longitudinal passage therein opening at the front end into a mouth for receiving the cables;

a tensioning head disposed within the jack body passage for one-to-one gripping of each cable, said tensioning head including (1) gripping means for gripping each cable, (2) unclamping means adapted for longitudinal movement relative to the gripping means from a disengaged position at which the unclamping means is inoperative to release the gripping means to an engaged position at which the unclamping means is operative to release the griping means, and (3) resilient means normally urging the unclamping means to the disengaged position;

a plate having a plurality of bores arranged in a pattern corresponding to that of the gripping means, the plate being adapted to be threaded onto the cables independently of the jack body and positioning closely adjacent the free ends of the cables to align the cables ends in the pattern of the gripping means so that the cable ends are held by the plate in proper alignment for receipt by the gripping means upon insertion of the jack body over the cables;

means for urging the tensioning head to a position adjacent the mouth of the jack body, so as to bring the plate and the tensioning head adjacent each other and to allow substantially simultaneous receipt of the cable ends by the gripping means upon insertion of the jack body over the cables, and for urging the tensioning head away from the housing to simultaneously tension the cables; and

means for engaging the plate to drive the anchor wedges into their corresponding wedge-shaped bores, whereby the cables are anchored to the structure in their tensioned state.

2. The jack according to claim 1 wherein the plate is dimensioned to be received axially within the mouth of the jack body.

3. The jack according to claim 1:

wherein the gripping means comprises a gripping plate having a plurality of wedge-shaped bores and gripping jaws for seating in the bores to grip the cables extending therethrough',

wherein the unclamping means includes means for selectively pulling the gripping jaws out of their corresponding bores in the gripping plate to release the cables from the gripping jaws; and the jack further including biasing means for urging the gripping jaws into their corresponding wedge-shaped bores.

4. The jack according to claim 1:

wherein the gripping means comprises a gripping plate having a plurality of wedge-shaped bores and gripping jaws for seating in the bores in the gripping plate to grip the cables extending therethrough; and wherein the tensioning head further includes means for urging the gripping jaws into their corresponding bores comprising a pressure plate having a plurality of bores arranged in a pattern corresponding with that of the gripping jaws and aligned therewith, the pressure plate being mounted to the rearward side of the gripping plate and spaced a predetermined distance therefrom, a tubular member coupled with the bases of the gripping jaws and extending through the corresponding bores in the pressure plate, and a spring means associated with each tubular member between the gripping jaws and the pressure plate.

5. The jack according to claim 4 wherein the spring means comprises a series of conical rings surrounding the tubular member.

6. The jack according to claim 4 further including a pulling plate mounted rearwardly of the pressure plate to the ends of the tubular members extending through the bores in the pressure plate and means for selectively pulling the pulling plate rearwardly to pull the jaws out of their corresponding bores in the gripping plate when the jack is to be removed from the cables after tensioning.

7. The hydraulic jack according to claim 3 wherein the biasing means includes a pressure plate in fixed spaced relation to the gripping plate, a plurality of tubular members each fastened to a gripping jaw and slidably extending through the pressure plate, the tubular members receiving the cables during tensioning, a plurality of conical rings each associated with and surrounding a tubular member between the jaws and the pressure plate, the conical rings alternately disposed so as to form a resilient assembly tending to bias the gripping jaws towards the corresponding bores in the gripping plate; and

the means selectively pulling includes a pulling plate having a plurality of bores arranged in a pattern corresponding to that of the gripping jaws and aligned therewith, the pulling plate axially positioned to the rear of the pressure plate and engaging the free ends of the tubular members, and means for moving the pulling plate rearwardly to pull the jaws out of their corresponding bores in the gripping plate.

8. A jack according to claim 1 wherein:

the gripping means includes a gripping plate having a plurality of wedge-shaped bores and gripping jaws for seating in the bores in the gripping plate to grip the cables extending therethrough; and

the unclamping means being adapted to coact with stop means located adjacent the mouth of the jack body, the unclamping means includes an unclamping plate having a plurality of hollow stubs, each mounted in a bore in the unclamping plate, the bores in the unclamping plate arranged in a pattern corresponding to that of the gripping jaws, the unclamping plate being slidably positioned axially in the passage and slidably attached to the gripping plate side closest to the mouth, the stubs being retained within the bores in the gripping plate to engage the gripping jaws and drive them out of their corresponding bores upon movement of the unclamping plate into engagement with the stop means.

9. A jack according to claim 1, wherein the tensioning head urging means includes:

a plunger attached to the tensioning head and slidable within the passage and having a bore to receive the cables, the plunger further having a first external step and the passage having a corresponding first internal step facing the first external step, the first external step and the first internal step forming the opposite ends of a first fluid-tight expansible pressure chamber between the plunger and the jack body, the plunger further having a second external step and the passage having a second internal step facing the second external step, the second external and the second internal step forming opposite ends of a second fluid-tight expansible pressure chamber between the plunger and the jack body;

means for introducing hydraulic fluid into the first pressure chamber to move the plunger away from the mouth to simultaneously tension the cables; and

means for introducing hydraulic fluid into the second pressure chamber to move the plunger into said position adjacent the mouth.

10. A jack according to claim 9, wherein the plate engaging means includes:

a striker piston having an external step and the passage having a corresponding third internal step facing the striker piston external step, the striker piston external step and the third internal step forming the opposite ends of a third fluid-tight expansible pressure chamber between the striker piston and the jack body; and

means for introducing hydraulic fluid into the third pressure chamber to move the striker piston towards the mouth to drive the anchor wedges into their corresponding bores in the anchor assembly.

11. A jack according to claim 1, wherein:

the tensioning head urging means includes a plunger slidable in the passage and having an annular shoulder defining a double acting piston and means for hydraulically driving the piston towards and away from the mouth of the jack body; and

the plate engaging means includes a single acting striker piston slidable in the passage adjacent the mouth thereof for driving the anchor wedges into their corresponding wedge-shaped bores in the anchor plate to anchor the cables, the striker piston having an external annular shoulder and the passage having a corresponding internal annular shoulder and the external and internal shoulders 7 9 forming the opposite ends of an annular expansible fluid-tight pressure space, and means for introducing hydraulic fluid into the annular space to move the striker piston toward the anchor plate to move the wedges into their corresponding wedge-shaped bores.

12. The jack according to claim 11 in which the working area of the face of the plunger piston which is effective to move the plunger away from the mouth is greater than the working area of the other face of the plunger piston which is effective to move the plunger back towards the mouth.

13. A jack for simultaneously tensioning a plurality of cables each projecting through a wedge-shaped bore in an anchor assembly and for anchoring the cables to a structure after tensioning by seating anchor wedges in the corresponding wedge-shaped bores, comprising:

a jack body having a front end for operatively abutting the structure during tensioning and further having a longitudinal passage therein opening at the front end into a mouth for receiving the cables;

a tensioning head mounted within the passage for movement longitudinally thereof;

gripping means carried by the tensioning head for gripping said plurality of cables, said gripping means including l a gripping plate having formed therein a corresponding plurality of wedge-shaped bores for receipt of the'cables and (2) gripping jaws adapted to be seated in the bores for gripping the cables to enable tensioning thereof;

unclamping means carried by the tensioning head for releasing the gripping jaws upon tensioning of the cables, said unclamping means including (1 an unclamping plate mounted on the side of the gripping plate nearest the passage mouth for limited longitudinal movement towards and away from the gripping plate and having formed therein a plurality of bores generally corresponding in number and arrangement to the bores of the gripping plate, (2) means carried by the unclamping plate in association with each bore and protruding therefrom towards the gripping plate for engagement, upon movement of the unclamping plate towards the gripping plate, with the gripping jaws in the corresponding gripping plate bore to force the jaws out of the bore, and (3) resilient means normally urging the unclamping plate away from the gripping plate;

means for moving the tensioning head longitudinally within the passage from a forward position at which it is adapted to receive the cables to a rearward position at which the cables are tensioned;

stop means located adjacent the passage mouth for limiting movement of the unclamping plate towards the mouth, whereby when the tensioning head is moved towards the mouth the unclamping plate moves corresponding until it is stopped by the stop means whereupon the gripping plate in continuing to move forward moves towards the unclamping plate such that the protruding means engage the gripping jaws and force them out of their corresponding bores in the gripping plates, thereby permitting the jack to be removed from the cables after tensioning; and

anchoring means carried by the jack body for driving the anchor wedges into the corresponding wedgeshaped bores, whereby the cables are anchored to the structure in their tensioned state, said anchoring means including an anchoring plate having a plurality of bores arranged in a pattern corresponding to the bores of the gripping plate, the anchoring vplate being adapted to be threaded onto the cables independently of the jack body and positioned closely adjacent the free ends of the cables to align the cable ends in the pattern of the gripping means so that the cable ends are held by the plate in proper alignment for receipt by the gripping means upon insertion of the jack body over the cables.

14. A jack for simultaneously tensioning a plurality of cables each projecting through a wedge-shaped bore in an anchor assembly and for anchoring the cables to a structure after tensioning by seating anchor wedges in the corresponding wedge-shaped bores, comprising:

a jack body having a front end for operatively abutting the structure during tensioning and further having a longitudinal passage therein opening at the front end into a mouth for receiving the cables;

a tensioning head mounted within the passage for movement longitudinally thereof;

gripping means carried by the tensioning head for gripping said plurality of cables, said gripping means including l a gripping plate having formed therein a corresponding plurality of wedge-shaped bores for receipt of the cables and (2) gripping jaws adapted to be seated in the bores for gripping the cables to enable tensioning thereof;

unclamping means carried by the tensioning head for releasing the gripping jaws upon tensioning of the cables, said unclamping means including (1 an unclamping plate mounted on the side of the gripping plate nearest the passage mouth for limited longitudinal movement towards and away from the gripping plate and having formed therein a plurality of bores generally corresponding in number and arrangement to the bores of the gripping plate, (2) means carried by the unclamping plate in association with each bore and protruding therefrom towards the gripping plate for engagement, upon movement of the unclamping plate towards the gripping plate, with the gripping jaws in the corresponding gripping plate bore to force the jaws out of the bore, and (3) resilient means normally urging the unclamping plate away from the gripping plate;

means for moving the tensioning head longitudinally within the passage from a forward position at which it is adapted to receive the cables to a rearward position at which the cables are tensioned;

stop means located adjacent the passage mouth for limiting movement of the unclamping plate towards the mouth, whereby when the tensioning head is moved towards the mouth the unclamping,

plate moves corresponding until it is stopped by the stop means whereupon the gripping plate in continuing to move forward moves towards the unclamping plate such that the protruding means engage the gripping jaws and force them out of their corresponding bores in the gripping plate, thereby permitting the jack to be removed from the cables after tensioning; and

means carried by the jack body for driving the anchor wedges into the corresponding wedge-shaped bores, whereby the cables are anchored to the structure in their tensioned state.

15. A method of simultaneously tensioning a plurality of cables extending from a structure with a jack having a plurality of gripping jaws in a tensioning head for oneto-one gripping of each cable comprising:

threading a plate having a plurality of bores arranged in a pattern corresponding to that of the gripping jaws onto the cables independently of the jack body;

positioning the plate closely adjacent the free ends of the cables to align the cable ends in the pattern of the gripping jaws;

positioning the tensioning head adjacent the front of the jack so that when the jack is mounted on the cables the tensioning head is adjacent the plate; inserting simultaneously all the aligned cables into the corresponding gripping jaws of the jack; actuating the gripping jaws to grip the cables; and moving the tensioning head rearwardly whereby the cables are simultaneously tensioned.

16. A method for simultaneously tensioning a plurality of cables extending from an anchor assembly having a wedge-shaped bore for each cable and anchoring the cables to the anchor assembly with a jack having a plurality of gripping jaws in a tensioning head for one-toone gripping of each cable comprising:

placing anchor wedges in each wedge-shaped bore in the anchor assembly;

threading a plate having a plurality of bores arranged in a pattern corresponding to that of the gripping jaws onto the cables independently of the jack body;

positioning the plate closely adjacent the free ends of the cables to align the cable ends in the pattern of the gripping jaws;

positioning the tensioning head adjacent the front of the jack so that when the jack is mounted on the cables the tensioning head is adjacent the plate; inserting simultaneously all the aligned cables into the corresponding gripping jaws of the jack; actuating the gripping jaws to grip the cables; moving the tensioning head rearwardly whereby the cables are simultaneously tensioned; and driving the plate against the anchor wedges after tensioning to seat the wedges in the corresponding wedge-shaped bores in the anchor assembly to anchor the tensioned cables to the anchor assembly.

17. A method of simultaneoulsy tensioning a plurality of cables extending from a structure with a jack having a jack body with a longitudinal passage therein opening at the front end into a mouth for receiving the cables and further having a plurality of gripping jaws disposed within the body passage for one-to-one gripping of each cable comprising:

threading a plate having a plurality of bores arranged in a pattern corresponding to that of the gripping jaws onto the cables independently of the jack body; positioning the plate closely adjacent the free ends of the cables to align the cable ends in the pattern of the gripping jaws; positioning the gripping jaws adjacent the front of the jack body so that when the jack is mounted on the cables the gripping jaws are adjacent the plate; inserting simultaneously all the aligned cables into the corresponding gripping jaws of the jack; actuating the gripping jaws to grip these cables; and

moving the gripping jaws rearwardly whereby the cables are simultaneously tensioned.

18. A method for simultaneously tensioning a plurality of cables extending from an anchor assembly having a wedge-shaped bore for each cable and anchoring the cables to the anchor assembly with a jack having a jack body with a front end for operatively abutting the anchor assembly during tensioning and further having a longitudinal passage therein and a plurality of gripping jaws disposed within the body passage for one-to-one gripping of each cable comprising:

placing anchor wedges in each wedge-shaped bore in the anchor assembly;

threading a plate having a plurality of bores arranged in a pattern corresponding to that of the gripping jaws onto the cables independently of the jack body;

positioning the plate closely adjacent the free ends of the cables to align the cable ends in the pattern of the gripping jaws;

positioning the gripping jaws adjacent the front end of the jack so that when the jack is mounted on the cables the gripping jaws are adjacent the plate;

inserting simultaneously all the aligned cables into the corresponding gripping jaws of the jack; actuating the gripping jaws to grip the cables; moving the gripping jaws rearwardly whereby the cables are simultaneously tensioned; and driving the plate against the anchor wedges after tensioning to seat the wedges in the corresponding wedge-shaped bores in the anchor assembly to anchor the tensioned cables to the anchor assembly. 

1. A jack for simultaneously tensioning a plurality of cables each projecting through a wedge-shaped bore in an anchor assembly and for anchoring the cables to a structure after tensioning by seating anchor wedges in the corresponding wedge-shaped bores, comprising: a jack body having a front end for operatively abutting the structure during tensioning, and further having a longitudinal passage therein opening at the front end into a mouth for receiving the cables; a tensioning head disposed within the jack body passage for oneto-one gripping of each cable, said tensioning head including (1) gripping means for gripping each cable, (2) unclamping means adapted for longitudinal movement relative to the gripping means from a disengaged position at which the unclamping means is inoperative to release the gripping means to an engaged position at which the unclamping means is operative to release the griping means, and (3) resilient means normally urging the unclamping means to the disengaged position; a plate having a plurality of bores arranged in a pattern corresponding to that of the gripping means, the plate being adapted to be threaded onto the cables independently of the jack body and positioning closely adjacent the free ends of the cables to align the cables ends in the pattern of the gripping means so that the cable ends are held by the plate in proper alignment for receipt by the gripping means upon insertion of the jack body over the cables; means for urging the tensioning head to a position adjacent the mouth of the jack body, so as to bring the plate and the tensioning head adjacent each other and to allow substantially simultaneous receipt of the cable ends by the gripping means upon insertion of the jack body over the cables, and for urging the tensioning head away from the housing to simultaneously tension the cables; and means for engaging the plate to drive the anchor wedges into their corresponding wedge-shaped bores, whereby the cables are anchored to the structure in their tensioned state.
 2. The jack according to claim 1 wherein the plate is dimensioned to be received axially within the mouth of the jack body.
 3. The jack according to claim 1: wherein the gripping means comprises a gripping plate having a plurality of wedge-shaped bores and gripping jaws for seating in the bores to grip the cables extending therethrough; wherein the unclamping means includes means for selectively pulling the gripping jaws out of their corresponding bores in the gripping plate to release the cables from the gripping jaws; and the jack further including biasing means for urging the gripping jaws into their corresponding wedge-shaped bores.
 4. The jack according to claim 1: wherein the gripping means comprises a gripping plate having a plurality of wedge-shaped bores and gripping jaws for seating in the bores in the gripping plate to grip the cables extending therethrough; and wherein the tensioning head further includes means for urging the gripping jaws into their corresponding bores comprising a pressure plate having a plurality of bores arranged in a pattern corresponding with that of the gripping jaws and aligned therewith, the pressure plate being mounted to the rearward side of the gripping plate and spaced a predetermined distance therefrom, a tubular member coupled with the bases of the gripping jaws and extending through the corresponding bores in the pressure plate, and a spring means associated with each tubular member between the gripping jaws and the pressure plate.
 5. The jack according to claim 4 wherein the spring means comprises a series of conical rings surrounding the tubular member.
 6. The jack according to claim 4 further including a pulling plate mounted rearwardly of the pressure plate to the ends of the tubular members extending through the bores in the pressure plate and means for selectively pulling the pulling plate rearwardly to pull the jaws out of their corresponding bores in the gripping plate when the jack is to be removed from the cables after tensioning.
 7. The hydraulic jack according to claim 3 wherein the biasing means includes a pressure plate in fixed spaced relation to the gripping plate, a plurality of tubular members each fastened to a gripping jaw and slidably extending through the pressure plate, the tubular members receiving the cables during tensioning, a plurality of conical rings each associated with and surrounding a tubular member between the jaws and the pressure plate, the conical rings alternately disposed so as to form a resilient assembly tending to bias the gripping jaws towards the corresponding bores in the gripping plate; and the means selectively pulling includes a pulling plate having a plurality of bores arranged in a pattern corresponding to that of the gripping jaws and aligned therewith, the pulling plate axially positioned to the rear of the pressure plate and engaging the free ends of the tubular members, and means for moving the pulling plate rearwardly to pull the jaws out of their corresponding bores in the gripping plate.
 8. A jack according to claim 1 wherein: the gripping means includes a gripping plate having a plurality of wedge-shaped bores and gripping jaws for seating in the bores in the gripping plate to grip the cables extending therethrough; and the unclamping means being adapted to coact with stop means located adjacent the mouth of the jack body, the unclamping means includes an unclamping plate having a plurality of hollow stubs, each mounted in a bore in the unclamping plate, the bores in the unclamping plate arranged in a pattern corresponding to that of the gripping jaws, the unclamping plate being slidably positioned axially in the passage and slidably attached to the gripping plate side closest to the mouth, the stubs being retained within the bores in the gripping plate to engage the gripping jaws and drive them out of their corresponding bores upon movement of the unclamping plate into engagement with the stop means.
 9. A jack according to claim 1, wherein the tensioning head urging means includes: a plunger attached to the tensioning head and slidable within the passage and having a bore to receive the cables, the plunger further having a first external step and the passage having a corresponding first internal step facing the first external step, the first external step and the first internal step forming the opposite ends of a first fluid-tight expansible pressure chamber between the plunger and the jack body, the plunger further having a second external step and the passage having a second internal step facing the second external step, the second external and the second internal step forming opposite ends of a second fluid-tight expansible pressure chamber between the plunger and the jack body; means for introducing hydraulic fluid into the first pressure chamber to move the plunger away from the mouth to simultaneously tension the cables; and means for introducing hydraulic fluid into the second pressure chamber to move the plunger into said position adjacent the mouth.
 10. A jack according to claim 9, wherein the plate engaging means includes: a striker piston having an external step and the passage having a corresponding third internal step facing the striker piston external step, the striker piston external step and the third internal step forming the opposite ends of a third fluid-tight expansible pressure chamber between the striker piston and the jack body; and means for introducing hydraulic fluid into the third pressure chamber to move the striker piston towards the mouth to drive the anchor wedges into their corresponding bores in the anchor assembly.
 11. A jack according to claim 1, wherein: the tensioning head urging means includes a plunger slidable in the passage and having an annular shoulder defining a double acting piston and means for hydraulically driving the piston towards and away from the mouth of the jack body; and the plate engaging means includes a single acting striker piston slidable in the passage adjacent the mouth thereof for driving the anchor wedges into their corresponding wedge-shaped bores in the anchor plate to anchor the cables, the striker piston having an external annular shoulder and the passage having a corresponding internal annular shoulder and the external and internal shoulders forming the opposite ends of an annular expanSible fluid-tight pressure space, and means for introducing hydraulic fluid into the annular space to move the striker piston toward the anchor plate to move the wedges into their corresponding wedge-shaped bores.
 12. The jack according to claim 11 in which the working area of the face of the plunger piston which is effective to move the plunger away from the mouth is greater than the working area of the other face of the plunger piston which is effective to move the plunger back towards the mouth.
 13. A jack for simultaneously tensioning a plurality of cables each projecting through a wedge-shaped bore in an anchor assembly and for anchoring the cables to a structure after tensioning by seating anchor wedges in the corresponding wedge-shaped bores, comprising: a jack body having a front end for operatively abutting the structure during tensioning and further having a longitudinal passage therein opening at the front end into a mouth for receiving the cables; a tensioning head mounted within the passage for movement longitudinally thereof; gripping means carried by the tensioning head for gripping said plurality of cables, said gripping means including (1) a gripping plate having formed therein a corresponding plurality of wedge-shaped bores for receipt of the cables and (2) gripping jaws adapted to be seated in the bores for gripping the cables to enable tensioning thereof; unclamping means carried by the tensioning head for releasing the gripping jaws upon tensioning of the cables, said unclamping means including (1) an unclamping plate mounted on the side of the gripping plate nearest the passage mouth for limited longitudinal movement towards and away from the gripping plate and having formed therein a plurality of bores generally corresponding in number and arrangement to the bores of the gripping plate, (2) means carried by the unclamping plate in association with each bore and protruding therefrom towards the gripping plate for engagement, upon movement of the unclamping plate towards the gripping plate, with the gripping jaws in the corresponding gripping plate bore to force the jaws out of the bore, and (3) resilient means normally urging the unclamping plate away from the gripping plate; means for moving the tensioning head longitudinally within the passage from a forward position at which it is adapted to receive the cables to a rearward position at which the cables are tensioned; stop means located adjacent the passage mouth for limiting movement of the unclamping plate towards the mouth, whereby when the tensioning head is moved towards the mouth the unclamping plate moves corresponding until it is stopped by the stop means whereupon the gripping plate in continuing to move forward moves towards the unclamping plate such that the protruding means engage the gripping jaws and force them out of their corresponding bores in the gripping plates, thereby permitting the jack to be removed from the cables after tensioning; and anchoring means carried by the jack body for driving the anchor wedges into the corresponding wedge-shaped bores, whereby the cables are anchored to the structure in their tensioned state, said anchoring means including an anchoring plate having a plurality of bores arranged in a pattern corresponding to the bores of the gripping plate, the anchoring plate being adapted to be threaded onto the cables independently of the jack body and positioned closely adjacent the free ends of the cables to align the cable ends in the pattern of the gripping means so that the cable ends are held by the plate in proper alignment for receipt by the gripping means upon insertion of the jack body over the cables.
 14. A jack for simultaneously tensioning a plurality of cables each projecting through a wedge-shaped bore in an anchor assembly and for anchoring the cables to a structure after tensioning by seating anchor wedges in the corresponding wedge-shaped bores, comprising: a jaCk body having a front end for operatively abutting the structure during tensioning and further having a longitudinal passage therein opening at the front end into a mouth for receiving the cables; a tensioning head mounted within the passage for movement longitudinally thereof; gripping means carried by the tensioning head for gripping said plurality of cables, said gripping means including (1) a gripping plate having formed therein a corresponding plurality of wedge-shaped bores for receipt of the cables and (2) gripping jaws adapted to be seated in the bores for gripping the cables to enable tensioning thereof; unclamping means carried by the tensioning head for releasing the gripping jaws upon tensioning of the cables, said unclamping means including (1) an unclamping plate mounted on the side of the gripping plate nearest the passage mouth for limited longitudinal movement towards and away from the gripping plate and having formed therein a plurality of bores generally corresponding in number and arrangement to the bores of the gripping plate, (2) means carried by the unclamping plate in association with each bore and protruding therefrom towards the gripping plate for engagement, upon movement of the unclamping plate towards the gripping plate, with the gripping jaws in the corresponding gripping plate bore to force the jaws out of the bore, and (3) resilient means normally urging the unclamping plate away from the gripping plate; means for moving the tensioning head longitudinally within the passage from a forward position at which it is adapted to receive the cables to a rearward position at which the cables are tensioned; stop means located adjacent the passage mouth for limiting movement of the unclamping plate towards the mouth, whereby when the tensioning head is moved towards the mouth the unclamping plate moves corresponding until it is stopped by the stop means whereupon the gripping plate in continuing to move forward moves towards the unclamping plate such that the protruding means engage the gripping jaws and force them out of their corresponding bores in the gripping plate, thereby permitting the jack to be removed from the cables after tensioning; and means carried by the jack body for driving the anchor wedges into the corresponding wedge-shaped bores, whereby the cables are anchored to the structure in their tensioned state.
 15. A method of simultaneously tensioning a plurality of cables extending from a structure with a jack having a plurality of gripping jaws in a tensioning head for one-to-one gripping of each cable comprising: threading a plate having a plurality of bores arranged in a pattern corresponding to that of the gripping jaws onto the cables independently of the jack body; positioning the plate closely adjacent the free ends of the cables to align the cable ends in the pattern of the gripping jaws; positioning the tensioning head adjacent the front of the jack so that when the jack is mounted on the cables the tensioning head is adjacent the plate; inserting simultaneously all the aligned cables into the corresponding gripping jaws of the jack; actuating the gripping jaws to grip the cables; and moving the tensioning head rearwardly whereby the cables are simultaneously tensioned.
 16. A method for simultaneously tensioning a plurality of cables extending from an anchor assembly having a wedge-shaped bore for each cable and anchoring the cables to the anchor assembly with a jack having a plurality of gripping jaws in a tensioning head for one-to-one gripping of each cable comprising: placing anchor wedges in each wedge-shaped bore in the anchor assembly; threading a plate having a plurality of bores arranged in a pattern corresponding to that of the gripping jaws onto the cables independently of the jack body; positioning the plate closely adjacent the free ends of the cables to align the cable ends in the pattern of the gripping jAws; positioning the tensioning head adjacent the front of the jack so that when the jack is mounted on the cables the tensioning head is adjacent the plate; inserting simultaneously all the aligned cables into the corresponding gripping jaws of the jack; actuating the gripping jaws to grip the cables; moving the tensioning head rearwardly whereby the cables are simultaneously tensioned; and driving the plate against the anchor wedges after tensioning to seat the wedges in the corresponding wedge-shaped bores in the anchor assembly to anchor the tensioned cables to the anchor assembly.
 17. A method of simultaneoulsy tensioning a plurality of cables extending from a structure with a jack having a jack body with a longitudinal passage therein opening at the front end into a mouth for receiving the cables and further having a plurality of gripping jaws disposed within the body passage for one-to-one gripping of each cable comprising: threading a plate having a plurality of bores arranged in a pattern corresponding to that of the gripping jaws onto the cables independently of the jack body; positioning the plate closely adjacent the free ends of the cables to align the cable ends in the pattern of the gripping jaws; positioning the gripping jaws adjacent the front of the jack body so that when the jack is mounted on the cables the gripping jaws are adjacent the plate; inserting simultaneously all the aligned cables into the corresponding gripping jaws of the jack; actuating the gripping jaws to grip these cables; and moving the gripping jaws rearwardly whereby the cables are simultaneously tensioned.
 18. A method for simultaneously tensioning a plurality of cables extending from an anchor assembly having a wedge-shaped bore for each cable and anchoring the cables to the anchor assembly with a jack having a jack body with a front end for operatively abutting the anchor assembly during tensioning and further having a longitudinal passage therein and a plurality of gripping jaws disposed within the body passage for one-to-one gripping of each cable comprising: placing anchor wedges in each wedge-shaped bore in the anchor assembly; threading a plate having a plurality of bores arranged in a pattern corresponding to that of the gripping jaws onto the cables independently of the jack body; positioning the plate closely adjacent the free ends of the cables to align the cable ends in the pattern of the gripping jaws; positioning the gripping jaws adjacent the front end of the jack so that when the jack is mounted on the cables the gripping jaws are adjacent the plate; inserting simultaneously all the aligned cables into the corresponding gripping jaws of the jack; actuating the gripping jaws to grip the cables; moving the gripping jaws rearwardly whereby the cables are simultaneously tensioned; and driving the plate against the anchor wedges after tensioning to seat the wedges in the corresponding wedge-shaped bores in the anchor assembly to anchor the tensioned cables to the anchor assembly. 